(1) Field of the Invention
The present invention relates to a cathodic sputtering device designed especially for coating articles of large size such as, for example, plates of glass.
Cathodic sputtering is a now well-proven technique for applying thin and uniform layers of a coating material to certain substrates. In general, cathodic sputtering is performed by means of a cathode connected to a source of electricity, the cathode being placed in an enclosure in a rarified atmosphere, in the presence of a gas (for example argon) whose nature varies depending on the required coating. A target made of the material to be sprayed and fastened to the cathode is bombarded with high-energy ions so that the particles of the material of which the target is made are torn away from the latter. The substrate to be coated is placed on the path of these particles and on it there forms a fine layer of the target material or of a chemical compound of the latter formed with the surrounding gas.
The possibility of confining the ions in the vicinity of the target by means of a magnetic field has led to considerable progress in this method by substantially increasing the rate of sputtering.
(2) Description of the prior art
A type of cathode is described in U.S. Pat. No. 3,956,093. This describes a plane target in which the magnetic devices are arranged so as to produce a confinement zone in the shape of an oval track.
A cathode of this type permits only singlesided sputtering. If the invention is to sputter both sides at the same time, then two cathodes must be placed with their backs close together, and this can involve the use of two separate supplies and make the process of controlling the deposit tricky.
Another sputtering cathode, for coating substrates of large size, is described in U.S. Pat. No. 4,971,196. In this cathode, two parallel target faces are connected by bridging faces in order to provide the continuity of the magnetic confinement belt. This cathode permits two opposing sides to be sprayed simultaneously, but it involves a relatively low speed of sputtering. To increase the rate of growth of the deposit, a number of cathodes of this type can be placed side by side in the same enclosure. Here too, separate supplied must be employed to obtain a homogeneous and reproductible deposit, and this greatly complicates the control process of the system.